Perspective drafting device



March 25, 1952 E HURST ETAL 2,590,252

PERSPECTIVE DRAFTING DEVICE Filed Oct. 30, 1948 'IIIIIIIIIIIIIIIIIIIIIII.

Patented Mar. 25, 1952 UNITED STATES PATENT OFFICE Edmund E. Hurst and John Warren Paxton,

Bloomington, Ill.

Application October 30, 1948, Serial No. 57,452

8 Claims.

This invention relates to a type of perspective drafting device disclosed in United States Patent No. 2,454,388, issued November 23, 1948.

The main objects of this invention are to provide an improved form of member which swingably mounts the straight edges of a drafting device of the afore-mentioned type which is adapted for attachment to a conventional type of drafting machine; to provide an improved mounting for the pivoted straight edges of such a drafting device which permits them to be interchanged from one side to the other of this mounting member in order to make differing scales on said straight edges available in the drawing of the divergent lines of the perspective figure; to provide an improved construction and arrangement of means for tensioning the normal freedom of the straight edges to swing on their pivots and for selectively holding said straight edges in fixed position during the drawing of lines therealong; to provide for such pivotally-mounted straight edges an improved form of scale with successively-diminishing graduations mathematically determined so as to permit the corresponding actual horizontal dimensions of an object to be measured along the respective straight edges; and to provide an improved perspective drafting device of this kind which is extremely simple in construction and design, attractive in appearance, light in weight, and positive in function.

In the accompanying drawings:

Fig. 1 is a plan view of a drafting board having mounted thereon a conventional type drafting machine to which is attached an improved perspective drafting device embodying this invention; the pulley-supporting clamps which simulate the vanishing points and support the tensioning spring for the swinging straight edges being mounted on the board in one of several possible relative positions;

Fig. 2 is a similar view but showing this improved perspective drafting device mounted on a conventional straight edge movable on the drafting board between the top and bottom edges thereof; the pulley-supporting clamps which simulate the vanishing points and support the tensioning spring for the swinging straight edges being shown mounted on the board in another of several possible relative positions;

Fig. 3 is a perspective view of this improved perspective drafting device;

Fig. 4 is an enlarged sectional view taken on the line 4-4 of Fig. 3;

Fig. '5 is a fragmentary detail as viewed from the plane of the line 5--5 of Fig. 4; and

Fig. 6 is a diagrammatical view indicating how the graduated scale on the pivoted straight edges may be used to lay off on a vanishing-point line the constantly reducing equivalents of the corresponding horizontal dimensions of the object for which the perspective is being drawn.

The preferred embodiment of a perspective drafting device, constructed in accordance with this invention, comprises a member I on which is mounted a fixed intermediate arm 8 and a pair of swingable arms 9 and I0 which respectively support straight edges II, I2, and I3, the latter two of which are adapted to be held in fixed positions, when drawinglines therealong, by means of levers I4 and I5 operating clamping means it (see Fig. 4). Such a device is adapted to be detachably mounted on a drafting machine I! of the type shown in Fig. 1 or in the form of a conventional straight edge such as is shown in Fig. 2, with the swingably-mounted straight edges I2 and I3 connected by a resilient element I8 which is kept in tension by two or more pulley-mounting clamps I9 adapted to be variously attached to a drafting board 20, thereby holding the straight edges I2 and I3 in proper relative angular positions to represent the diverging horizontal lines of the object to be drawn in perspective on the drafting board 20.

The mounting member 1 comprises a base plate 2| and a head block 22 which are held together by three screws 23 so as to support the arms 8, 9, and I0, and levers I4 and I5, and the clamping means IS.

The base plate 2I is provided with a chuck 24 and a clamp 25 (see Fig. 3) whereby this perspective drafting device is detachably mountable on a drafting machine, as shown in Fig. 1. The base The middle straight-edge supporting arm 8, as

will most clearly appear from Fig. 5, is T-shaped. The transverse part of the T extends parallel to and abuts the flange 26 on the head block 22.

The stem of the T extends forwardly of the mounting member I.

The straight-edge supporting arms 9 and III are mounted on pivot pins 28 and 29 (see Figs. 4

apertures 32 formed in the respective scales II, I2, and I3. (See Fig. 4.)

Each of the straight edges II,'I2, and I3 is formed with a decimal scale 34 along one side and a fractional or binary scale 33 along the other side. The scales 33 and 34 along the middle straight edge I I are the standard 12-inch length. However, the scales 33 and 34, along the opposite edges of the straight edges I2 and I3 are provided with successively-diminishing graduations mathematically determined and permit the corresponding actual horizontal dimensions of an object, for which a perspective view is being made, to be measured along the respective straight edges I2 and I3. These perspective scales 33 and 34 are formed of such length that when the device is moved on the drafting board 2| so that the position on the scale registers with the 16 position on the drafting board, with the straight edge in alinement with the previously-drawn line from 0 to 16, the 16 major graduations on the scale constitute the equivalent of 32 corresponding measurements of the actual object. Similarly, if the scale is subsequently advanced into an equivalent third position, the major divisions on the scale represent a corresponding 64 divisions on the object of which the perspective is being made. It is. apparent, therefore, that the actual distances represented in perspective by successive lengths of the. scales 33 and 34 increase by a geometric progression which, in the illustrated case, has a ratio of 2. This relationship permits the accurate scaling of perspective dimensions greater than the length of the perspective 'scales, and facilitates the execution of larger drawings withoutrequiring complex conversion calculations. This feature of the perspective scales is diagrammatically indicated in Fig. 6. As will be noted, the scales 33 and 34 on the straight edges I2 and I3 are respectively decimal, and fractional or binary, i. e., being graduated so that each subdivision of the unit is half the size of the next larger subdivision, as is common with the ordinary inch scale.

The levers I4 and I5 each comprise an arm 35, a hub 36, and a thumb or finger pad 31. The hub parts 36, of the respective levers I4 and I5, are set in recesses 38 in the head block 22 of the mounting member I on pivot pins 39 extending transversely of the axes of the swingable straightedge supporting arms 9 and II]. The thumb pads 31 on the two arms 35 extend inwardly toward each other and by virtue of the pivotal mounting of the levers I4 and I5 on the head block 22 and pads31 are in a convenient position to be depressed by the thumb or a finger on either hand of the draftsman.

The clamping means I5 whereby the straight edges I2 and I3 are retained in position against accidental displacement during the drawing of a line therealong, comprises for each arm 9 and I 3 a friction pad 40, a disk 4|, a ball 42, a pin 43, and a tension nut 44 on the threaded pin 23.

The friction pad 44 extends over practically the entire area of the under surface of the head block 22 and the opposed surfaces of the'straightedgesupporting arms's, 9, and I9.

The disks M are concentrically arranged over each of the respective pivot pins 29 and 30. The disks M are either apertured or recessed to provide a seat for the respective ball 42 against which abuts the lower end of the respective pin 43.

The pins 43, as will most clearly appear in Fig. 4, are threaded into the hub 35 so as to be adjusted to vary the pressure applied against the ball 42 for depressing the disk 4I' into contact with the friction pad 40, and consequently the pressure applied against the respective arms 9 and I0.

The knurled nuts 44, for each of the levers l4 and I5, permit an adjustment of the pressure of the pins 43 against the respective balls 42, and

consequently against the arms 9 and I0. These nuts 44 separately permit an adjustment of the minimum pressure of the disks 4I against the respective arms 9 and I0 so as to regulate the free. swinging. of, said arms.

As shownin the above mentioned United States Patent No- 2,454,388, the flexible element I8 is preferably in the form of a coil spring. The ends of the spring are detachably connected to the ends of the straight edges I2 and I3, bayonet slots 45 (see Fig. 3) being formed in the outer ends of the straight edges I2 and I3 for that purpose. The pulley-supporting clamps I9, by which the flexible element I8 is held in tension, may be of any convenient form that will permit their attachment to the drafting board 20 in various positions so that at least two of them represent the vanishing points for a' perspective drawing.

The operation of this perspective drawing device is more or less obvious from the foregoing description.

Once the device is clamped to the drafting machine or straight edge I I and the pulley clamps I9 are appropriately arranged, any movement of the drafting machine or the straight edge I! over the drafting board 20 causes the straight edges I2 and I3 to swing into various angular positions with respect to each other and to the vanishing points so as to represent the corresponding horizontal linesof the object of which the perspective drawing is being made.

At any time when the device has been positioned for drawing lines along the straight edges l2 and I3, one or both ofthe straight edges may be held against accidental displacement, during the drawing of the line, by a slight pressure of the thumb or finger against one or both of the thumbpads 3! for the levers I4 and I5. Such depression of the levers will further press the pins 43 against the balls 42, and consequently increase the pressure of the disks 4I against the friction pad 40 and in' turn against the respective arms 9 and ID.

The straight edges I2 and I3 may be mounted on either of the arms 9 and I0 so as to permit the use of either the decimal or fractional perspective scale.

Any variations or modifications in the details of the structure and arrangement of the parts may be resorted to within the spirit and coverage of the appended claims.

We claim:

1. In a device of the class described the combination of, a recessed mounting member, a scale-supporting arm, a pivot pin supporting said arm in said recess to permit the swinging of said arm in the plane of said member, a

straight edge attached; to said arm, a lever hinged on said 'member above said arm on an axis transverse to the'axis of said pivot pin, a disk superimposed on said arm, a ball supported; on said disk and exposed through an aperture in said member, and a shoulder on said lever off set from the hinge thereof and contacting said ball whereby the depression of said lever causes said disk to be so pressed against said arm as to hold said straight edge against displacement when a line is being drawn therealong. Y

,2. In a device of the class described the combination of, 'a recessed mounting member, a scale-supporting arm, a pivot pin supporting said arm in said recess to permit the swinging of said arm in the plane of said member, a straightedge attached to said arm, a lever hinged on said member above said arm on an axis transverse to the axis of said pivot pin, a disk superimposed on said arm concentrically of said pivot pin, a ball supported on said disk coaxially with said pivot pin and exposed through an aperture in said member above said recess, and a threaded pin on said lever off set from the hinge thereof and axially alined and positioned with the end thereof in contact with said ball whereby the depression of said lever causes said disk to be so pressed against said arm as to clamp said straight edge against displacement when a line is being drawn therealong.

3. In a device of the class described the combination of, a recessed mounting member, a scalesupporting arm, a pivot pin supporting said arm in said recess to permit the swinging of said arm in the plane of said member, a straight edge attached to said arm, a lever hinged on said member above said arm on an axis transverse to the axis of said pivot pin, a disk superimposed on said arm concentrically of said pivot pin, a ball supported on said disk coaxially with said pivot pinand exposed through an aperture in said member above said recess, a threaded pin on said lever off set from the hinge thereof and axially alined and positioned with the end thereof in contact with said ball whereby the depression of said lever causes said disk to be so pressed against said armas to clamp said straight edge against displacement when a line is being drawn therealong, a third pin fixed on said member and extending upwardly through a bore in said lever, and a knurled nut adjustable on said pin for determining a minimum pressure of said disk on said arm so as to regulate the free swinging of said arm on said member.

4. In a device of the class described the combination of, a recessed mounting member, a scalesupporting arm, a pivot pin supporting said arm in said recess to permit the swinging of said arm in the plane of said member, a straight edge at tached to said arm, a lever hinged on said member above said arm on an axis transverse to the axis of said pivot pin, a friction pad superimposed on said arm, a, disk superimposed on said friction pad concentrically of said pivot pin, a ball supported on said disk coaxially with said pivot pin and exposed through an aperture in said member, and a shoulder on said lever oif set from the hinge thereof in alinement with said pivot pin and contacting said ball whereby the depression of said lever causes said disk to be so pressed against said friction pad as to clamp said straight edge against displacement when a line is being drawn therealong.

5. In a perspective drafting device of the class described the combination of, a mounting member provided with recesses extending inwardly from its forward corners in the plane of said member, a pair of arms, pivot pins supporting said arms in the respective member recesses to permit the swinging of said arms in the plane of said member, a straight edge attached to each of said arms, a lever pivoted on said member above each of said arms on an axis transverse to the axis of the respective arm pivot, a friction pad superimposed on said arms, a disk superimposed on said friction pad concentrically of each of said pivot pins, a ball supported on each of said disks and exposed through apertures in said member, and a shoulder on each of said levers off set from the hinge thereof and contacting the respective ball whereby the depression of a lever causes the respective disk to be so pressed against said friction pad as to hold the respective straight edge against displacement when a line is being drawn therealong.

6. In a perspective drafting device of the class described the combination of, a mounting member provided with recesses extending inwardly from its forward corners in the plane of said member, a pair of arms, pivot pins supporting said arms in the respective member recesses to permit the swinging of said arms in the plane of said member, a straight edge attached to each of said arms, a lever pivoted on said member above each of said arms on an axis transverse to the axis of the respective arm pivot, a friction pad superimposed on said arms, a disk superimposed on said friction pad concentrically of each of said pivot pins, a ball supported on each of said disks and exposed through apertures in said member, and a threaded pin on each of said levers arranged in axial alinement with the respective pivot pins and engaging the respective balls whereby the depression of one of said levers is adapted to so press the respective disk against the corresponding arm as to clamp the straight edge against displacement when a line is being drawn therealong.

'7. In a device of the class described, the combination of a mounting member, an arm pivotally attached to said member, a straight edge attached to said arm, a lever pivoted on said member above said arm on an axis transverse to the axis of the pivotal mounting of said arm, friction means interposed between said lever and said arm, a shoulder on the underside of said lever adapted to press said friction means against said arm when said lever isdepressed thereby to prevent swinging movement of said arm, said shoulder being adjustable toward and away from said lever, and an abutment connected to said member and engageable with the upper side of said lever, said abutment being adjustable toward and away from said member for regulating the minimum pressure of said friction means on said arm, said shoulder being disposed intermediate said abutment and said transverse axis.

8. In a drafting device of the class described, the combination of a mounting member, an arm pivotally attached to said member, a straight edge attached to said arm, a lever attached to said member above said arm for pivotal movement about an axis transverse to the axis of the pivotal mounting of said arm, friction means interposed between said lever and said arm, a shoulder on the underside of said lever adapted to press said friction means against said arm when said lever is depressed thereby to prevent swinging movement of said arm, and an abutment connected to said member and engageable :zgonmamv with theiuppervside oil said lever, saidabutmenti" being adjustable toward and; awayxfrom; said;

, Number member for regulatmg the?mlmmumnpressureof 763-419 said friction .meansionxsaid arm, said shoulder 1 9865506 being disposed: intermediate said. .abutmentiandi 5 250297899 saidlittansverse .axis; 2- 171008 JOHN WARREN PAXTON.

REFERENCES CITED m e r Number The followmgreferences are of record m the 691 file of this patent:

Name Date Ofi'erman June 28, 1904 Harris Jan. 1, 1935 Stem Feb. 4, 1 936- Garner Oct; 8, 1940 Gbff Nov; 23, 1948 FOREIGN PATENTS Country Date Great Britain .Aug. 26; 1947 

